Conference "Cellulosic biocomposites and nanomaterials" by Lars Berglund

The rapid development of nanoscience and nanotechnology of cellulose nanofibrils (CNF) has inspired industrial technologies as well as intense academic research efforts. Progress in chemical functionalization of CNFs, understanding of cellulose-cellulose interactions, polymer-cellulose interfaces in composites, colloidal CNF behavior and the use of CNF in functional materials are some examples. Although CNFs are often presented as eco-friendly, the cumulative energy demand to prepare CNF materials is in many cases very high. For this reason, it is of interest to consider the possibilities to better utilize the intrinsic nanostructure of plant fibers as well as wood. Delignification becomes essential since this is a route by which the specific surface area of the plant cell wall (“inner surface”) may be increased. This facilitates efficient chemical functionalization of cellulose microfibrils in the plant cell wall. In addition, mildly delignified wood fibers and wood tissue have been demonstrated to have better mechanical properties than typical data reported in the literature. Reasons for this are discussed.
A particular case of nanostructured cellulose biocomposites is so called transparent wood biocomposites. The pore space of delignified wood is filled with a polymer of matching refractive index. As a consequence, the total optical transmittance can be very high, at least for thin specimens. Mechanisms for light scattering are discussed and some examples of applications as functionalized photonic materials are presented. The general role of the cellulose/polymer interface is discussed in some detail, based on microscopic as well as molecular scale effects. The strive for high optical transmittance has stimulated better appreciation for the criticality of nanoscale dispersion of CNF or microfibrils. CNF polymer matrix composites based on well-dispersed fibrils can show improved optical transmittance and consistent improvement in Young’s modulus with cellulose content.
At the end, an attempt will be made to summarize the lessons learned for cellulosics in terms of eco-friendly materials, mechanical property potential, functionalization approaches and why homogeneous distribution of discrete cellulose nanofibrils is important for physical properties.

Hôte : Yoshiharu Nishiyama (CERMAV)
 

Lars Berglund
Professor and director of Wallenberg Wood Science Center
KTH Royal Institute of Technology
SE-10044 Stockholm, Sweden